Field of the Invention
The present invention provides various uses of electromagnetic interference patterns, and particularly (but not exclusively) to uses of visible light interference patterns, UV interference patterns and IR interference patterns. Typical uses disclosed herein relate to spatial metrology, such as a translational and/or angular position determination system, and to methods for such position determination. Further uses include the analysis of properties of the electromagnetic radiation itself (such as the determination of the wavelength of the electromagnetic radiation). Still further uses include the analysis of one or more properties (e.g. refractive index) of the matter through which the electromagnetic radiation passes.
Related Art
U.S. Pat. No. 4,111,557 discloses a method for determining the shape or position of an object with respect to the shape or position of a reference object. The reference object may be a master object, a scale model, or an ideal object which is determined only by computation or graphically, or it may be the same object observed at a different time.
In U.S. Pat. No. 4,111,557, light rays from a coherent source are projected as lines and/or point arrangements onto an object using lenses. These lines or point arrangements are transferred to an optoelectronic recording device (e.g. a TV camera or a photodiode matrix) by means of an objective lens. The signals produced by the recording device are converted into digital data for storage and for comparison with the data corresponding to the reference object.
Other known optical positioning systems are discussed below.
WO2004/031686 discloses a laser interferometer system providing position feedback. The interferometer system disclosed in WO2004/031686 requires an external retroreflector target optic and measures changes of position along the axis of the light beam.
WO02/084223 and EP0503176 disclose optical positioning systems using scales that encode absolute position information. It is also known to provide an optical positioning system in which an LED illuminates a periodic linear scale and the reflected light is detected and analysed. The device determines the relative position between the scale and the read-head, which contains the LED and detector.
WO 2006/067481 discloses a 2D pattern and a sensor, moveable relative to one another. The pattern (e.g. an array of dots) is arranged as groups of features, each group encoding an absolute position. For example, one dot of each group may have a distinctive colour for identifying the position of that group.